1. Field of the Invention
This invention relates to a multiposition precision joystick type control device useful, for example, in the control of vehicles of various sorts, such as underwater and surface craft, off road vehicles and aircraft, as well as in such applications as plotting boards and radar controls.
2. Description of the Prior Art
Joystick type control devices have found relatively wide application in the control of various machines and in particular in the control of vehicles. One particularly useful control device of this type has a digitally or manually controlled actuator which is movable in any lateral direction with respect to a first axis to cause flexure of flexible bar means having transducer means attached thereto. The transducers are responsive to flexure of the flexible bar means along a pair of orthogonally related second and third axes. Typically the transducers are piezoresistive strain gauges made of semiconductor material the resistivity of which changes when exposed to deformation forces. The strain gauges are incorporated into a bridge circuit, and the change in resistivity thereof is effective to differentially unbalance the bridge. Thus, compression or tension of the strain gauges caused by lateral displacement of the actuator provides a coordinate-related electrical output corresponding to the forces applied to the actuator along the second and third axes. Such electrical output is supplied to electroresponsive control means which provides a desired controlling function to apparatus to be controlled.
Because of the fragility of semiconductor type strain gauges, resort has been had in the past to the use of stop shoulders, typically adjustable stop screws, to limit the degree of flexure to which the flexible bar means having strain gauges attached thereto can be subjected. However, in precision applications, such expedients are not practical because of the extremely tight tolerances which are required.
Representative of the joystick type control devices of the prior art are those disclosed in the following U.S. patents: Palfreyman U.S. Pat. No. 3,447,766; Woodworth et al. U.S. Pat. No. 3,924,458; Vaiden et al U.S. Pat. No. 3,473,760; Colston U.S. Pat. No. 4,216,467, Rothweiler et al U.S. Pat. No. 3,666,900, and Strandh U.S. Pat. No. 3,832,895.
While the joystick type control devices of the prior art have found numerous applications, there is need to provide improved control devices which are multimodal and perform additional functions, are of small size and are of sealed precision construction. Moreover, there is need in such a control device to provide means for preventing operation in more than one mode at a time, as well as to provide means for preventing transducer damage in the event of application to the actuator member of a lateral force in excess of a predetermined magnitude.